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To Stretch Something
If 伸びる is "to be stretched" then 伸ばす is to stretch something, where you're doing the stretching. You know this because you took a bus and you stretched it out to be an even longer bus.
The reading comes from 伸びる, so if you know that you should know this.
My grandmother reached her hands up to my face and told me "I love you," right before she passed away.